If you have the Morolians in your Character Profile screen, the first six will inform you of who to talk to in order to learn about the hidden commands for each mission. If you've accomplished the hidden commands that each person tells you about, the relevant Morolian will tell you who to talk to next until you've learned about all the hidden commands.
The most important thing to be learned from the Morolian process is this: you CANNOT get the achievement simply by getting 100% on each level. There is one critical exception: when doing the cheerleader section in Report 4, if you've saved all of the cheerleaders there will be 24 hidden commands to hit. If you've missed even a single one, there will be only 16 to hit. These commands are tracked separately; you MUST complete both sets in order to trigger the achievement. Therefore, you must do both a run where you save all the cheerleaders and a run where you miss at least one cheerleader.
Some additional information:
#1 - this is at the end of "mine," not the beginning. If you tap the button in time with the beat, you'll get it (as well as #2)
#2-6 - if you've saved all of the Rescue Squad, they do a little chant during which the word "Hrk" appears on the screen five times; this is where you press to hit the commands. Again, if you're tapping along to the beat, you'll hit them. If you haven't saved all of the Rescue Squad the words don't appear, but you can still hit the hidden commands
#7 - right after the "tuned" in "Stay tuned"
#8 - at the cheer after saving the cheerleaders (meets the common music pattern seen in most levels)
#9-32 - to get all 24 of these, you must have saved all the cheerleaders. After the rescue, they start a series of cheers where they chant "go go" etc. Just tap along to the beat during this entire sequence and you'll hit them all. If you've missed any of the cheerleaders you can still do this, but the cheer will be different and there will be only 16 commands to hit
#33 - when Ulala and Space Michael pose after Space Michael is saved
#1 - this is at the beginning of where Pudding/Padding says "tuned," not the end
#2-5 - there are four band members who strike poses for hidden commands (all but Ulala). Just tap along with the beat, you'll hit them
#3 - the command is at the "t" sound in "lost" during the phrase "When have I ever lost... at dancing"